1. Field of the Invention
The present invention relates to impeller pumps of a type known as Westco pumps, generative or friction pumps, cascade pumps and circumferential-flow pumps that have rotary impellers.
2. Description of the Related Art
A known Westco pump is shown in FIGS. 23 and 24, in which the Westco pump includes a single impeller 110 disposed rotatably within a pump casing 104. The impeller 110 has a substantially circular disk-like configuration and rotates as a shaft 109a of an armature of a motor section (not shown) rotates. A predetermined number of grooves 112 are formed in each of upper and lower surfaces of the impeller 110 and are arranged at a predetermined pitch in the circumferential direction. The grooves 112 formed in the lower surface and the grooves 112 formed in the upper surface are arranged symmetrically with each other. Thus, the grooves 112 formed in the lower surface and the grooves 112 formed in the upper surface are arranged at the same circumferential positions with each other.
Referring to FIG. 23, the pump casing 104 defines pump channels 151 and 171 that oppose to the grooves 112 formed in the upper surface and the grooves 112 formed in the lower surface of the impeller 110, respectively. Suction ports 152 and 172 are defined in communication with start ends of the pump channels 151 and 171, respectively. Discharge ports 153 and 173 are defined in communication with terminal ends of the pump channels 151 and 171, respectively. As shown in FIG. 24, the suction port 152 and the discharge port 153 of the pump channel 151 are separated from each other by a partition wall 105a that defines an interruption region. Similarly, the suction port 172 and the discharge port 173 of the pump channel 171 are separated from each other by a partition wall 107a. A fuel suction channel 170 is defined in the pump casing 104 and is open into a suction side region. The fuel suction channel 170 communicates with the suction ports 152 and 172. A fuel discharge channel 150 is defined in the pump casing 104 and is open into a discharge side region. The fuel discharge channel 150 communicates with the discharge ports 153 and 173. Incidentally, as shown in FIG. 24, the discharge ports 153 and 173 are disposed at the same position with each other in the circumferential direction of the impeller 110.
Referring to FIG. 23, in order to perform a pumping operation, the impeller 110 is rotated, so that a fuel is drawn from the suction side through the fuel suction channel 170. Subsequently, the fuel is diverged into the inlet ports 152 and 172 and then enters the pump channels 151 and 171. The fuel that has entered the pump channels 151 and 171 receives kinetic energies from the grooves 112 (i.e., fins defined by the grooves 112) of the impeller 110 and is pressurized to be fed through the pump channels 151 and 171. The fuel that has been fed to the terminal end of the pump channel 151 and the fuel that has been fed to the terminal end of the pump channel 171 are converged after passing through the discharge ports 153 and 173, respectively. The fuel is then discharged via the fuel discharge channel 150.
However, in the known Westco pump, the grooves 112 formed in the lower surface and the grooves 112 formed in the upper surface are arranged at the same positions in the circumferential direction of the impeller 110. In addition, the discharge port 153 of the pump channel 151 and the discharge port 173 of the pump channel 171 are disposed at the same position in the circumferential position of the impeller 110. Therefore, the phase of pulsation of the fuel discharged from the pump channel 151 and the phase of pulsation of the fuel discharged from the pump channel 171 are the same with each other, and the pulsations of fuel may be intensified by the convergence of the fuel discharged from the discharge ports 153 and 173. As a result, pump noises that may be caused by the pulsations may increase. Here, the term “pulsation” is used to mean a periodic change in pressure of the fuel during the operation of the pump.
Furthermore, in the known Westco pump, the directions of flow of the fuel from the pump channels 151 and 171 are changed at substantially right angles toward the discharge ports 153 and 173, respectively. Therefore, the fuel collides with corner portions 151a and 171a (see FIG. 24) at the terminal ends of the pump channels 151 and 171. Pump noises also may be increased due to impacts caused by this collision. Therefore, it has been desired to reduce pump noises that may be caused by the pulsations and the impacts of the fluid.
Japanese Laid-Open Patent Publication Nos. 3-18688, 8-14814 and 2000-329085 teach Westco pumps having impact reduction means. However, these publications relate to Westco pumps in which a fluid is drawn from a suction port disposed on one side of an impeller and is then discharged from a discharge port disposed on the other side of the impeller. The impeller has a plurality of grooves that are formed in each of upper and lower surfaces of the impeller and are spaced from each other in the circumferential direction by a predetermined pitch. The impact reduction means is provided for reducing impacts of the fluid, which impacts may be produced when the direction of the flow of the fluid is changed toward the discharge port. Thus, the Westco pumps of the publications are not configured to discharge the fluid from two discharge ports that are disposed on both upper and lower sides of the impeller. Therefore, the publications do not teach reduction means that is designed or intended to reduce the pulsations of the fluid that may be intensified due to the convergence of the fluid discharged from the discharge ports.